2017ApJ...846..139M

We investigate the intracluster light (ICL) in the six Hubble Frontier Field clusters at 0.3 z 0.6. We employ a new method, which is free from any functional form of the ICL profile, and exploit the unprecedented depth of this Hubble Space Telescope imaging to map the ICL's diffuse light out to clustrocentric radii R∼300 kpc (µ_ICL∼27 mag arcsec^–2). From these maps, we construct radial color and stellar mass profiles via SED fitting and find clear negative color gradients in all systems with increasing distance from the Brightest Cluster Galaxy (BCG). While this implies older/more metal-rich stellar components in the inner part of the ICL, we find that the ICL mostly consists of a 2 Gyr population, and plausibly originated with logM_*/M_☉ 10 cluster galaxies. Furthermore, we find that 10%-15% of the ICL's mass at large radii ( 150 kpc) lies in a younger/bluer stellar population (∼1 Gyr), a phenomenon not seen in local samples. We attribute this light to the higher fraction of star-forming/(post-)starburst galaxies in clusters at z∼0.5. Ultimately, we find the ICL's total mass to be logM_*^ICL/M_☉∼11-12, constituting 5%-20% of the clusters' total stellar mass, or about half of the value at z∼0. The above implies distinct formation histories for the ICL and BCGs/other massive cluster galaxies; i.e., the ICL at this epoch is still being constructed rapidly (∼40 M_☉ yr^–1), while the BCGs have mostly completed their evolution. To be consistent with the ICL measurements of local massive clusters, such as Virgo, our data suggest mass acquisition mainly from quiescent cluster galaxies is the principal source of ICL material in the subsequent ∼5 Gyr of cosmic time.